[FIX] opw584557: account: better default fiscalyear dates for fiscalyears not 1/1-12/31
[FIX] use correctly datetime objects
[IMP] better comment
[IMP] account: use DEFAULT_SERVER_DATETIME_FORMAT
[IMP] account: use DEFAULT_SERVER_DATETIME_FORMAT and merging in one method
[IMP] account: compute default period for fiscal year
[MERGE] opw584557: account: use current and previous fiscal year for account.config.settings